The invention relates to a camshaft adjuster for an internal combustion engine according to the preamble of Claim 1.
Camshaft adjusters can be classified generally as follows:
A. Phase adjuster with an actuating element, that is, a functional unit that engages in the mass flow or energy flow, which is constructed, for example, hydraulically, electrically, or mechanically, and which rotates with drive elements of the camshaft adjuster.
B. Phase adjuster with a separate actuator, that is, a functional unit, in which the actuating parameter necessary for regulating the actuating element is formed from the regulator output parameter, and a separate actuating element. Here, there are the following constructions:
a. Phase adjuster with a co-rotating actuator and a co-rotating actuating element, for example, a high ratio gear drive, whose adjustment shaft can be advanced by a co-rotating hydraulic motor or centrifugal force motor and which can be retarded by a spring.
b. Phase adjuster with a co-rotating actuating element and a stationary, motor-fixed actuator, for example, an electric motor or an electric or mechanical brake, see also DE 100 38 354 A1, DE 102 06 034 A1, EP 1 043 482 B1.
c. Phase adjuster with a directionally dependent combination of the solutions according to a. and b., for example, a motor-fixed brake, in which a portion of the brake power is used, for example, for adjusting toward an advanced position, in order to tension a spring, which enables the retarding adjustment after the brake is deactivated, see also DE 102 24 446 A1, WO 03-098010, US 2003 0226534, DE 103 17 607 A1.
In systems according to B.a. to B.c., the actuator and actuating elements are connected to each other by an actuating shaft. The connection can have a configuration that is switchable or non-switchable, detachable or non-detachable, clearance-free or burdened with clearance, and flexible or stiff. Independent of the construction, the adjustment energy can be realized by the provision of a drive and/or brake power, as well as by use of loss powers of the shaft system (e.g., friction) and/or moments of inertia and/or centrifugal forces. Braking can also take place, advantageously in the “retarded” adjustment direction, under complete use or co-use of the friction power of the camshaft. A camshaft adjuster can be equipped with or without a mechanical limit of the adjustment range. As a gear drive in a camshaft adjuster, one-stage or multiple-stage triple-shaft gear drives and/or multiple linkage or coupling gear drives are used, for example, in constructions as wobble-plate gear drives, eccentric gear drives, planetary gear drives, undulating gear drives, cam plate gear drives, multiple linkage or coupling gear drives or combinations of the individual constructions for a multiple-stage configuration.
While conventional, hydraulically actuated camshaft adjusters or camshaft adjusters in configurations with vane cells, pivot vanes, or segment vanes have the advantage that                the hydraulic medium can be fed into the camshaft adjuster at any point for actuation,        the hydraulic medium is fed further into the camshaft adjuster via suitable flow channels,        the hydraulic medium—if necessary—can be reversed, and        suitable devices for actuating the hydraulic pressure can also be arranged eccentric to the camshaft adjuster,in conventional camshaft adjusters, in which the actuating movement is generated by an electric motor and a variable ratio gear drive, triple-shaft gear drive, or planetary gear drive (in the following, variable ratio gear drive), see, e.g., DE 41 10 195 A1, the electric motor is typically arranged before the variable ratio gear drive aligned with the longitudinal axis of the camshaft and the variable ratio gear drive. For this reason, such camshaft adjusters with an electrical actuating assembly and a variable ratio gear drive are built axially larger than corresponding hydraulically actuated camshaft adjusters.        
From DE 37 37 602 A1, it is known to use a differential gear drive as a variable ratio gear drive, in which drive is realized by means of a drive wheel in drive connection with the crankshaft and a driven part to the camshaft aligned with the longitudinal axis, while the feeding of the drive movement of the electrical actuating assembly is realized radial to the previously mentioned longitudinal axis.
From DE 102 60 546 A1, a hydraulic camshaft adjuster is known, to which a vacuum pump can be coupled on the side facing away from the camshaft aligned with the longitudinal axis.
DE 38 30 382 C1 discloses the drive of a planetary gear drive mounted axially before a variable ratio gear drive using an electrical actuating assembly, whose longitudinal axis is offset parallel to the longitudinal axis of the camshaft and the variable ratio gear drive.
The variable ratio gear drive known from U.S. Pat. No. 4,747,375 is constructed as a planetary gear drive, in which, for a first construction, the ring gear is driven by a servomotor, whose longitudinal axis is arranged parallel to the longitudinal axis of the camshaft, while the sun wheel of the planetary gear drive is in drive connection with the crankshaft of the internal combustion engine and the planetary gear drive is driven relative to the camshaft by a connecting piece. For an alternative construction, the drive is realized using the servomotor and the sun wheel for an aligned orientation of the servomotor relative to the longitudinal axis of the camshaft, while the crankshaft drives the ring gear by driving the connecting piece of the planetary gear drive.
Finally, DE 103 52 255 A1 discloses a coupling of an electrical actuating assembly via a flexible shaft, a pneumatic motor, a hydromotor, so that the actuating assembly can be arranged at any point. Furthermore, from the publication the proposal is to be taken to arrange an electrical actuating assembly parallel to the camshaft and to arrange a gear stage between the variable ratio gear drive and the electrical actuating assembly.